The present apparatus is directed to a system for measuring the concentration of chlorine flowing in a process stream. Chlorine is a strong reactant which is handled in process plants only in specifically contructed pipes and conduits. Because of its strong chemical nature, it typically is contained under specially made devices with safe guards to prevent escape. The strong chemical activity of chlorine makes it difficult to obtain measurements of chlorine. That is, it is not quite so easy to obtain access to the chlorine to make flow or volume measurements as might be required. A particularly important requirement in the handling of chlorine in large processing plants where chlorine is either manufactured or used is measurement of the concentration of chlorine. The process stream typically includes some kind of conduit connecting some source of chlorine either with a storage tank or alternatively with a process using the chlorine. Attempts have been made in the past to make such measurements. One such device is set forth in U.S. Pat. No. 2,286,985. This device sets forth a phototube arrangement. A more recent device is a smoke detector utilizing cylindrical light transmitting rods of about 1/2" in diameter. This is shown in U.S. Pat. No. 3,976,891. Two U.S. patents by Zimmerman (U.S. Pat. Nos. 3,968,006 and 4,152,073) are also directed to chlorine measurement systems. A laser transmitted along a pipe is set forth in U.S. Pat. No. 4,421,408. It is believed that none of these references either singly or collectively set forth the improved system of this disclosure for measuring chlorine concentration.
This apparatus incorporates a means for measuring concentration without difficulties arising from invasion of the pipe where the chlorine flows. Rather, chlorine attack on the measuring apparatus is limited by the use of an impervious lens. The lens is particularly able to prevent unwanted entry of chlorine or damage arising from it. Further, a comparative technique is utilized wherein light of two separate wavelengths is transmitted through the chlorine. A particular wavelength is selected where the light is absorbed by the chlorine while another wavelength is selected where chlorine absorption is substantially nil. The second wavelength light is used as a reference. This reference is particularly valuable to remove errors which might arise as a result of lamp aging. It also overcomes errors that might occur with degradation of the light transmission path over a period of time. To the degree that degradation does occur, it impacts equally both wavelengths so that the reference is likewise degraded. This enables relative measurements against the reference whereby aging and degradation factors are substantially eliminated.
A particularly important advantage of the present apparatus is the positioning of the light source and analyzing equipment remote from the pipe or conduit in which the chlorine is flowing. Mounting immediately on the pipe is not required. If convenient, it certainly can be mounted on the pipe but the equipment can likewise be mounted elsewhere. The equipment incorporates a light source which must be periodically changed. For this reason, it may be appropriate to locate the light source convenient for personnel and to extend optical fibers from the lamp to the pipe or vessel. This enables a measure of adaptability and improves the mounting of the apparatus.
With the foregoing advantages in view, the present apparatus is briefly summarized as a chlorine concentration measuring system including a housing having a light source therein emitting light in a specified spectrum. A rotating optical filter is included. Preferably, it passes two wavelengths. One wavelength is selected to substantially pass through the chlorine. The second wavelength is preferably about 3600 angstroms which wavelength is absorbed by chlorine. That is, the chlorine is opaque to this wavelength by an amount or in a measure determined by the concentration of chlorine. The light is emitted, passed to the filter, and travels along an optical fiber. The optical fiber is tipped by a sapphire lens in a housing mounted in the wall of the pipe for projecting a beam of light across the pipe. A similarily mounted optical fiber on the opposite side protected by a similar sapphire lens receives the light beam. The light passing through the chlorine is then transmitted through the optical fiber to a photometric detector. The signal is supplied to a processor for conversion into calibrated data. As appropriate, this can be connected with a recorder.